(1) The tidal cycle and that of solar elevation interact to produce patterns in seabed irradiance during the day which change over the springs-neaps cycle. In locations where high water springs is at midday, there is a single peak in seabed irradiance in the middle of the day at neap tides and two peaks in seabed irradiance (one in the morning, the other in the evening) at spring tides.

(2) These cycles also interact to produce a springs–neaps cycle of daily mean irradiance, which is relevant to the growth of benthic algae. The pattern of this cycle will also vary from place to place. In locations where low water springs is in the middle of the day the pattern is straightforward: maximum daily irradiance always occurs at spring tides. However, where high water springs is in the middle of the day, the cycle can reverse as the days get longer. The timing of the switch in the cycle depends upon the water clarity.

(3) Variations in attenuation over the springs–neaps cycle will also be important. In the Menai Strait, a springs–neaps cycle in K is often (but not always) observed, higher attenuations occurring at spring tides when seabed sediments are stirred up by the stronger tidal currents. This will reduce seabed irradiance at spring tides and tend to favour greater irradiance at neaps. In our model runs, K was kept constant because at present it is difficult to predict these changes. However, in our observations there is evidence of greater seabed irradiance at neap tides associated with greater water clarity. Variations in cloud cover during the day can also affect the regular cycles predicted by the model.

The authors are grateful to Professor Ernest Naylor for encouragement and for information on animal behaviour and light. Members of the Marine Optics Group at Menai Bridge helped with the sampling during the experimental work in July 1994.

Forty-three species of choanoflagellates were seen during a study of the heterotrophic nanoflagellates in Southampton Water, between 1991 and 1994. The majority of the species were loricate choanoflagellates (Acanthoecidae), and this group accounted for –8% of the total heterotrophic nanoplankton during the period of study. Aloricate choanoflagellates (Codosigidae and Salpingoecidae) were less diverse, and accounted for only 3–4% of the heterotrophic nanoplankton. The seasonal occurrence of loricate choanoflagellates was studied using light microscope whole mounts, whilst more detailed studies of lorica structure were made using electron microscope whole mounts. Two new species, described in this paper, had a markedly seasonal occurrence and were only recorded during a period of 6–10 weeks each spring.

Laboratory experiments were carried out upon Elphidium crispum to determine the mechanism by which this species remains epifaunal, by investigating geotaxism, phototaxism, temporal influence and responses through ontogeny. Different size-classes of specimens were tested for phototaxism and geotaxism, over four and five months respectively. Specimens of the smallest size-class tested (250–355 μm) were significantly phototaxic and geotaxic. Significant positive phototaxism was demonstrated in all tests except one, with specimens in the size-class 500–1000 μm giving particularly significant results for the months of June and July 1994. Specimens were significantly geotactic for three of thirteen tests: both negative and positive geotaxism were demonstrated.

Xenophyophores are a group of giant deep sea protists characterized by intracellular barium sulphate (BaSO4) crystals. X-ray diffraction, electron diffraction and electron microscopy studies have been performed on barium sulphate crystals from three xenophyophore species (Aschemonella ramuliformis, Reticulammina labyrinthica, Galatheammina lamina) obtained at bathyal and abyssal depths in the north-eastern Atlantic. Two populations of crystals were observed. The first were tablets, ~2μm in length and rhombic or hexagonal in outline. In both cases, the tabular face was of index (100). The second population consisted of much smaller particles (<0·5 μm) of poor crystallinity. A comparison of the larger xenophyophore crystals with synthetically grown crystals indicated that the former probably grew at low supersaturation (S<25) in solutions of low to moderate ionic strength (I<l·0 M). Some preliminary observations of the cellular organisation of A. ramuliformis are reported. The protoplasm is multinucleate and characterized by what seems to be a system of extracellular lacunae formed by imaginations of the cell wall. Similar features have been observed in the deep sea foraminiferan Rhizammina algaeformis. Possible origins of the BaSO4 crystals and the taxonomic relationship between xenophyophores and certain foraminiferans are discussed.

Six species of naked amoebae, ranging in size from 45 to 3258 μm3, were isolated from benthic sediments of the Clyde Sea area. The number of fluorescently labelled bacteria (FLB) consumed by these amoebae was determined at 5, 10, 15 and 20°C. Consumption rates varied markedly, ranging from 0·2 to 194·7 bacteria h−1 (equivalent to 0·16–155·8 μim3 bacterial biomass). However, only some of these values were considered to be optimal; several of the uptake values were too low to account for the measured growth rates of amoebae. Using the optimal consumption rate data, the mean specific rates increased from 0·042 bacteria h−1 μm3 at 5°C to 0·131 bacteria h−1 μm−3 at 20°C. This is the first study to detail the ingestion rates of a range of bacterivorous marine gymnamoebae.

The vertical distribution, morphology and diet of Proboscidactyla stellata (Cnidaria: Limnomedusae) were studied in Lough Hyne over a two year period. Vertical hauls of four depth strata, 40–30 m, 30–20 m, 20–10 m and 10–0 m, were taken monthly and at 4 h intervals for a period of 48 h in July and 24 h in September 1994. Proboscidactyla stellata was largely concentrated in the lower 20 m of the water column reaching a maximum of 21 m−3 at 30–20 m depth in June 1993. An oxythermocline occurred at 25–30 m depth in the summer and autumn months of 1993 and affected the vertical distribution of the medusae. Six morphs of the species, varying in the number of gonads, were found in the lough. Bivalve veligers, which P. stellata actively selected, formed 83% of the diet.

The Porcupine Abyssal Plain in the north-eastern Atlantic Ocean is subject to periodical deposition of phytodetritus and has a highly diverse benthic fauna dependent on this source of organic matter. Among the most abundant species from the northern study site of the Institute of Oceanographic Sciences Deacon Laboratory (IOSDL) at ~48°50′N 16°30′W, 4850 m, is Iosactis vagabunda gen. nov., sp. nov. (Cnidaria: Actiniaria, Iosactiidae fam. nov.), a small endomyarian sea anemone. The fact that this species is a burrower, with a smooth, unspecialized column, and a rounded aboral end provided with a central pit, makes it stand out from the other families of endomyarian anemones and prompted the establishment of the new family Iosactiidae. There is evidence that the closest relatives of the new family are the ‘deep water actiniids’ (e.g. Bolocera, Liponema, Leipsiceras), and the Andresiidae. Long-term in situ time-lapse photographs indicate a unique behaviour of this anemone in that it moves out of its hole at times, presumably exhibiting a hemisessile lifestyle in this peculiar abyssal habitat.

The dynamics of egg production by a Mediterranean population of the terebellid polychaete Eupolymnia nebulosa was assessed both in the field and in the laboratory between 1992 and 1994. Our results confirm the occurrence of several peaks of jelly mass production at the population level. They show that such peaks result from the production of several broods per individual female (the number of produced broods increasing with female size). Jelly masses produced at the end of the breeding season tend to be smaller and to contain fewer eggs than those produced at the beginning of the breeding season. Worms produced significantly larger jelly masses in 1994 than in 1993 and 1992, without noticeable change in corresponding fecundities. The computation of temporal changes in eggs produced per unit of surface area in the cove of Paulilles shows that most of the eggs are produced during the first two peaks of jelly mass production. These results are discussed relative to the different hypotheses invoked to account for the occurrence of several spawnings in Mediterranean populations of E. nebulosa. It is concluded that no single explanation, such as the allometry constraint hypothesis or heterogeneity in oogenesis rates, can be retained.

Genome size (or C-value) in benthic polychaetes was studied from both experimental data and literature. Nuclear DNA content variation was analysed as related to both phylogenetic relationships of various families, general life habit of the species (interstitial vs macrobenthic), diploid chromosome number (2n), and mean body size (length). Experimental data on genome size were obtained for 43 lower taxa (genera and species) by means of microdensitometric analysis of the amount of Fuelgen-stained haploid DNA in interphase nuclei. These data, added to those available in the literature (36 taxa studied by Conner et al., 1972) gave a total of 79 taxa (genera and species), representing 30 families and 14 orders. Twenty-one of the species studied belonged exclusively to interstitial (=meiofaunal) families or genera.

Dyopedos monacanthus inhabits self-constructed mud whips on marine soft-bottoms. Juveniles stay on the mud whip of their mother for extended time periods after they hatch from her brood pouch. During the main reproductive period in the spring, parental females have been observed in the aquarium and collected from the field. Specimens of D. monacanthus have been collected simultaneously from the intake filter from the sea-water laboratory. Several consecutive clutches have been found on the whip of one female. Most juveniles are small (1 mm in size), but they grow to sizes of >2 mm on the whip of their mother. In the aquarium, juveniles usually hatched immediately after the females had been attended by males. They then clung to their mother's whip for about two weeks. Most parental females in the aquarium produced three broods during a time period of about six weeks. In the field an average of 36 parental females m-2 were found in April, and an average number of 75 juveniles clung to each female's whip. The average number of juveniles found on the females’ whips declined in May and June. Many juveniles appeared in the sea-water intake filter starting in mid April. Most juveniles caught in the intake filter were between 2 and 3 mm in size which corresponds well with their size at leaving the female's whip. In mid May, all amphipods disappeared within a few days from the aquarium, when shrimp Crangon septemspinosa started to become more active again. Many big females disappeared in the field at that time too, and in mid June parental females were smaller than in the previous months. The amphipod D. monacanthus belongs in the category of epibenthic suspension-feeding amphipods. It is probably very susceptible to epibenthic predation and extended parental care is primarily a mechanism to lift very small juveniles above the viscous sublayer in the benthic boundary layer.

The cirral activity of the penduculate barnacle, Conchoderma auritum, was studied in a flow tank. The barnacles were exposed to different experimental water velocities and the response of the barnacles was recorded using a video system. In still and slow-moving water the barnacles show rhythmic cirral activity, the cirri extend and then withdraw into the mantle cavity. When water flow is accelerated the barnacles switch from rhythmic cirral activity to prolonged cirral extension, in which the cirri are extended in the water flow, facing the current. The water velocity at which barnacles switch from rhythmic activity to cirral extension depends on the size of the animal. During the rhythmic activity of Conchoderma water is pumped into the mantle through the ears. The prosoma serves as a piston which inhales the water into the capitulum and then ejects it at the apical end of the capitulum opening. This finding contradicts the generally accepted notion that the function of the ears of C. auritum is water ejection.

The digestive system of the thalassinidean mud-shrimp Upogebia stellata was investigated using scanning electron microscopy (SEM). Within the lumen of the midgut both filamentous and rod-shaped bacteria were observed. The hindgut microbial populations were dominated by dense mats of epimural rod-shaped bacteria. The gut contents were often dominated by diatoms but also contained bacteria, dinoflagellates, plant and algal fragments. Direct bacterial counts by epifluorescence microscopy along the length of the gut revealed a slight decrease in numbers within the midgut moving from the anterior to the posterior regions, and then a dramatic rise in numbers within the hindgut. Numbers decreased again in the posterior regions of the hindgut. Common in the transient / resident samples (bacterial population when gut contents were present) were enterobacteria and an unidentified fermenter conforming to an isolate named X-ferm. However, nearly 30% of the bacterial isolates remained unidentified. The resident-only bacterial isolates from the gut (determined when the gut was empty) were dominated by the X-ferm bacteria and to a lesser extent by the genera Vibrio and Aeromonas. With respect to the enzyme capabilities of the gut bacteria, the resident-only collection of bacterial isolates showed much higher levels of amylase, cellulase, chitinase, protease and lipase activity than the transient/resident bacterial isolate collections, suggesting that the indigenous bacteria are likely to play a significant role in the digestion of the gut contents. Thalassinidean shrimps are likely to play an important role in the breakdown of plant and detrital material, and the recycling of nutrients in marine benthic systems.

The bresiliid shrimp Alvinocaris markensis is a predator that inhabits the base of sulphide mounds built by the black smoker chimneys of active hydrothermal vents at the Snake Pit site on the Mid-Atlantic Ridge. Casual examination of animals collected with theDSV ‘Alvin’ suggests that, like other biesiliid shrimp from hydrothermal vents, the eyes of this species are adapted for vision in very dim light. However, examination of the structure and ultrastructure of eyes of animals collected and immediately fixed shows that the expected massive array of photoreceptors is partially or completely missing. The eye is enlarged, its dioptric apparatus has disappeared, its screening pigment is essentially gone, and its reflecting pigment cells have formed an enlarged mass of white diffusing cells behind the expected layer of photoreceptors. In half of the animals examined, there were no recognizable photoreceptors in the retina, and in the remaining animals there were only scattered photoreceptors with poorly organized microvillar arrays of photosensitive membrane. We conclude that this species is blind despite some retinal adaptations for vision in very dim light. Apparently, the ambient light of this animal's environment is below the quit point (the minimum level that can be exploited) so that the retina has begun to degenerate by losing its photoreceptors.

Recent attention to members of the sepiolid squid genus Euprymna and symbiotic associations with luminescent bacteria (Vibrio fischeri strains) has prompted a review of this poorly-resolved group of squids. Twelve nominal species have been placed in this genus of which the majority are ill-defined, known only from their original descriptions and separated on the basis of inadequate characters. As a first step in resolving this group, a temperate Australian species, the Southern dumpling squid, Euprymna tasmanica, is here redescribed in detail. As the genus Euprymna currently stands, most members are only distinguished on the number and position of enlarged suckers in mature males. No diagnostic characters are available to identify females. All nominal species placed in this genus are reviewed and a key to proposed valid species is presented. Six species are considered here to be valid: Euprymna berryi, E. hoylei, E. morsei, E. scolopes, E. tasmanica and an undescribed species treated here as Euprymna sp. 1. Euprymna similis is a synonym of E. morsei of Japan. Due to inadequate original descriptions, and lost or poor type material, two species are considered here to be nomen dubia (E. schneehageni and E. pusilla), while the taxonomic status of four additional species remain unresolved (E. albatrossae, E. bursa, E. phenax and E. stenodactyla).

Allozyme electrophoresis was used to estimate the genetic divergence between three species of South African Helcion and the north-east Atlantic H. pellucidum (Patellidae). At a finer level the genetic relationships among South African Helcion were explored. Twenty-one loci were resolved for all the species. High values of expected heterozygosities (0·202–0·341) were found for the genus. Phenetic analysis (UPGMA (unweighted pair-group method with artihmetic averaging) and Distance Wagner Procedure) and cladistic parsimony methods (alleles as binary characters and loci as multistate unordered characters) agreed in showing the same topology for the tree which represents the genetic relationships among Helcion species. The north-east Atlantic H. pellucidum was the most divergent species showing high values of Nei's genetic distances (1·423–1·654) with its South African congeners. In the literature such values of genetic divergence have been associated with non-congeneric species. The degree of genetic divergence (0·351–0·615) found within the South African branch was characteristic for congeneric species. The results of this study supported the monophyletic condition of this branch, and showed H. pectunculus and H. pruinosus to be more closely related to each other than to H. dunkeri. Nevertheless, the monophyly of the genus Helcion is uncertain and therefore its taxonomic status was questioned. A possible independent origin for northern and southern hemisphere species of Helcion is considered.

Side-scan sonar and underwater video were used to determine the impact of a trawl fishery on an epibenthic community associated with the horse mussel, Modiolus modiolus in a Northern Ireland sea lough. The presence of marks caused by trawl otter-boards on the sediments could be clearly seen using side-scan sonar and changes to the epibenthos are described from the video survey. It is apparent from the side-scan sonar survey that changes have occurred in the structure of the superficial sediments on heavily trawled areas. However, there was no clear indication of temporal changes. The utility of side-scan sonar coupled with GIS techniques to detect temporal and spatial effects is discussed.

The spatial distribution and temporal variations of the Abra alba-Pectinaria koreni community from the eastern part of the Bay of Seine were investigated through four winter surveys (1986, 1987, 1988 and 1991). A grid of 40–67 stations was sampled each year using a Hamon grab (0·25 m-2) for macrofauna collection and sediment analysis. The fauna was dominated by polychaetes and in a lower part by molluscs and echinoderms. Although species richness with ~100 species collected during each survey was high, total density and biomass (±SE) resulted principally from about ten dominant species, and varied between 846·9 ±163·5 and 1135·3 ±186·7 ind m-2 and 23·52 ±4·41 and 27·48 ±4·45 g m-2respectively. The dominant species were patchily distributed and exhibited weak spatio-temporal fluctuations except the two bivalves A. alba and Cultellus pellucidus. Factorial correspondence analysis (FCA) of the distribution of main species among stations and automatic hierarchical classification identified five faunal assemblages which were relatively stable in space and time. The temporal stability of the community could be generated by processes of larval retention near parental population, and sediment stabilization induced by the low abundance of deposit feeders and the high densities of the tube-dwelling polychaete Owenia fusiformis. While the sediment variables were a poor indicator of the spatial structure of the community, the salinity gradient off the Seine Estuary and post-settlement processes (e.g. food limitation and postlarval drifting) have been proposed to explain it. Comparison with an earlier survey (i.e. 1971) suggested a degree of long-term persistence of the community structure in qualitative and quantitative terms.

Cadmium was rapidly concentrated by Mytilus galloprovincialis (Mollusca: Bivalvia) during one week's exposure to 0–5 ug Cd ml-1 sea-water. Cadmium accumulation was determined in the gills, adductor muscle and viscera. The amount of cadmium bound to metallothionein (MT) provided a specific index of exposure to this metal. Maximum values were reached in viscera; this observation is consistent with the presence, in the viscera, of the hepatopancreas which is commonly regarded as a major site for MT synthesis. In tissues of M. galloprovincialis exposed to Cd different energy charge (AEC) responses were observed. Adenylate energy charge (AEC) values appeared to be more affected by Cd exposure in adductor muscle than in the gills and viscera. These variations could be related to an impairment of oxidative metabolism leading to a partial switch from aerobic to anaerobic metabolism. The data obtained from anoxic incubation did not show significant differences in AEC values between pre-exposed and untreated animals, with the sole exception of adductor muscle of exposed mussels.

Growth of the echinoid Sphaerechinus granularis from the Gleiian Islands (Brittany, France) was studied by analysis of growth zones in longitudinal cross-sections of interambulacral oral plates. The diameter-at-age data pairs were increased using a back-calculation technique, which allows for a more efficient estimation of von Bertalanffy growth curve parameters. The annual value of the skeletal growth marks agreed with the analysis of the population's size-frequency distributions taken from a previous study. Significant differences in growth and morphological parameters were observed between two populations of the archipelago in close geographical proximity and inhabiting the same type of substratum. These differences, which appear as population phenotypic responses to different hydrodynamic conditions, confirms growth plasticity in S. granularis.

Six colour varieties were recognized in an intertidal population of Amphipholis squamata from Normandy (France). Each variety exhibits its own capacity to produce light, the light emitted by the most luminous variety being 500 times more intense than that emitted by the least luminous one. Differences in luminescent capabilities observed between varieties do not seem to be due to differences in pigmentation or to be of exogenous origin. It was shown that the capability to produce light changes according to whether individuals are brooding or not, brooding individuals emitting a more intense light than non-brooding ones. This supports the defensive use of luminescence generally associated to ophiuroid production of light. However, light capabilities differ so much between A. squamata colour varieties that bioluminescence could also be associated with another role in the species.